"We're reminding motorists they should avoid the city core if at all possible. We're encouraging motorists to remain calm and for riders to remain respectful of the rules of the road and the safety laws," he said.

McKenna said the event also has him concerned about trouble.

"Critical Mass was originally designed as a protest over the lack of bike lanes," he said.

"It's now morphed into a major celebration. Unfortunately, it's also morphed into a source of major conflict between riders and the driving public. Last month, we saw an increase in the violence that frequently mars the ride."

McKenna blames both sides for the trouble, but said it could be avoided if the event's organizers would share their plans with police.